In a memory module, a test device is provided as a part of the memory chips which store information. The test unit is integrated on the respective memory chip and carries out an electrical functional test before the memory chip is mounted on the printed circuit board, in order to guarantee, before the actual mounting process, that the memory chip operates without any errors. During the functional test, which is carried out in each case internally within the memory chip, information is written to memory addresses and read from the latter, written and read information being compared with one another. A further functional test is carried out after the mounting of the memory chips on the printed circuit board, in which case the memory module is connected to an external tester. This tester is able to generate the test commands for testing the memory module, i.e., control commands, address commands, and data values to be stored, and the clock signal, which typically lies in the region of a few 100 MHz. With the aid of corresponding lines through which the memory module is connected to the external tester, the electrical functional test is then repeated in cross-memory-chip fashion, each memory chips usually being tested in parallel at the same time. This second functional test provides information about whether the electrical contact connections between the respective memory chips and the printed circuit board function satisfactorily.
External testers of this type have many parallel lines which are connected to the memory module and by which a large number of complex memory tests can be programmed. These connecting lines include data lines for each memory chip, corresponding control lines, which are generally simultaneously address lines, and also a clock line, which provides the required clock signal.
The connecting lines between the tester and the memory module are exposed to external ambient influences, i.e., electromagnetic fields, which can distort and corrupt the test signals in the MHz range. Moreover, the electrical contact connection of the memory module through many dozens of leads is complicated. On the other hand, a memory test downstream of the chip mounting process cannot conventionally be carried out differently, because only one external tester generates the test signal and the test commands, which simultaneously enable a functional test of all the memory chips of the memory module.